Catch trout and protect native species

Posted on September 23, 2013

The introduction of salmon and trout to areas outside their natural range often puts pressure on native fish species, which suffer increased predation, habitat displacement and reduced growth.   In the Southern Hemisphere, introduced salmonids have been linked to contractions in the distribution of native fish such as galaxiids (jollytails), but many details of the ecological interactions between salmonids and galaxiids remain unclear.  Researchers collected fish samples from 25 Chilean lakes, 17 of which had been invaded by rainbow and brown trout in 1968-70, and used differences in fish body composition – specifically, concentrations of the stable isotope 15N derived from food – to compare rainbow trout, brown trout and native galaxiids (Galaxias platei ) in terms of their position on the food chain.  They found that when trout were abundant, the  coexisting galaxiids tended to feed lower on the food chain.  And when galaxiid densities were low, large trout fed lower on the food chain.  These findings suggested that the feeding success and growth of galaxiids was reduced by competition from trout, but also that the resulting impact on the galaxiid population in turn limited the feeding success of trout.  The researchers proposed that the best management strategy would be to cull trout from overpopulated lakes, which  should simultaneously protect native fish and support a sport fishery for large trout.

Reference:   Correa, C., Bravo, A.P. & Hendry, A.P.  2012.   Reciprocal trophic niche shifts in native and invasive fish: salmonids and galaxiids in Patagonian lakes.  Freshwater Biology 57, 1769–1781.